According to the text, the main reason for the imbalance in studies of media content and studies of ...

According to the text, the main reason for the imbalance in studies of media content and
  studies of media effects about stereotypes is:

a. Research with human subjects is messier than research with media messages.
  b. Researchers feel obliged to document the presence or absence of media content
  prior to doing a study on media impact.
  c. Media content studies are generally more important than media effects studies.
  d. Media effects studies are generally more important than media content studies.
  e. Documenting media effects is considerably more difficult than documenting the
  presence or absence of media content